Dielectric material and method of making the same



Patented Mar. 31, 1942 DIELECTRIC us'rlnm AND m!) OI mama m ssru:

IugeneWainerandNorman-I-Thielke,

Falls,N.Y.,assignorto Tho-'litanimfilcy Manufacturing company, New York. N. 1., a oorporationofllaine N0 Drawing. Application 11111 4, 1939, Serial N0. M1.

' a cum. (on. roe-4e) This invention relates to ceramic dielectric materialsandthemethodofmakingthesame. More particularly it relates to such materials in which titanium dioxide is the predominant constituent.

This application is a continuation in part of our ccpending application Serial No. 270,462, filed April 2'1, 1939. In the aforesaid copending application the method of forming and firing such dielectric material was pointed out in detail. In addition, the disadvantages of certain impurities in titanium dioxide when intended to be used as a dielectric were also pointed out. Finally, it was pointed out that there were certain advantages in adding the titanates of the alkaline earth metals, calcium, barium and strontium.

It is an object of this invention to produce a titanium dioxide ceramic of improved characteristics. It is a further object to utilize directly naturally occurring rutiles in the formation of ceramic bodies of excellent dielectric characteristics. It is a further object to provide a method for forming ceramic bodies of excellent dielectric characteristics. Other objects will appear hereinafter.

These objects are accomplished by incorporating in a ceramic dielectric body, containing principally titanium dioxide, one or more of a certain group of titanates. The titanates which are useml in this connection are of the alkaline earth elements (calcium, strontium and barium), cadmium, zinc, boron anddivalent lead. The most useful of these are strontium, barium, cadmium, boron and divalent lead.

In our above mentioned copending application the disadvantages of certain impurities in titanium dioxide, when used for dielectric purposes,

were pointed out. Among the most harmful of these impurities is vanadium. For example, a rutile ceramic dielectric containing no titanates and prepared as described below showed a resistivity about one thirtieth that of a heavy grade titanium dioxide ceramic dielectric containing no titanates and also prepared as described below. The difference is probably caused in good part by the much larger quantity of vanadium in the rutile body. This is borne out by experiments with bodies containing vanadium titanate. These were prepared exactly as in Examples 3 and 4 below, respectively, except that vanadium titanate (VrTiO-z) was used in place of strontium titanate and the peak temperatures employed were 2400 F. and 2500" F. respectively. Both bodies showed a resistivity of less than 100 megohms (the upper limit of the measuring instrument used) andextremely high power factors (over 15%). On the other hand. the dielectric constantswere quitehigh,and,inthe caseof the heavy grade titanium dioxide body, increased quite markedly with increase of temperature. The following. table shows these relationships:

Tam I Vanadium titanate bodies G. Rutila Rutile ggf 11x0, 2. r. K

Percent Percent 10. a 100. 8 20. 0 10a. 0 17. a 107. 0 20. a 101. 9 1a a 102. 7 21. 4 101. 2 rs. a 107. 5 22. 5 02. 3 2s. 1 112. 0 22. 1 7s. 5 s2. 0 116. 5 18.6 59. 0 so. a 121. 0 19. 5 55. 1 41. 0 127. 3 17. 4 40. 4 47. 6 136. 7 19. 8 41. 6

It has now been found that the harmful effect of these impurities, and particularly vanadium, can be minimized by adding to the ceramic body one or more of the titanates of calcium, barium, strontium, cadmium or divalent lead. At the same time other valuable dielectric properties can be secured by adding to the ceramic body one or more of the above titanates or zinc titanate or boron titanate. In general, the quantity of such titanate is preferably between 3% and 20% of the entire ceramic composition. Amounts below 3% are relatively ineffectual and amounts above 20% have the following disadvantages: production of higher shrinkages; difiiculty of maintaining proper purity and uniformity, due to the fluxing action of the titanates; difiiculty of preventing warpage; development of gas porosity due to bubbling, and sometimes an adverse eifect on the dielectric constant. The particle fineness of the titanates should be comparable to that of the titanium dioxide base.

The particle size of the titanium dioxide base is also of importance in securing the best results. Materials containing particles of a lower maximum size (1. e. finer particles) are more suitable for several reasons: They are much easier to controlon firing; the values obtained are more uniform; the temperature range of satisfactory vitrification is broadened; there is less tendency towards crystallization; there is less porosity; and the effect of impurities is minimized. Best results are also secured by firing the ceramic dielectric to a temperature such as to secure maximum vitreous structure with substantially no crystalline growth.

We have also tried certain other titanates, with much less useful results, and in some cases with results that are positively harmful. For example, a body prepared as in Example 2 below, except that magnesium titanate is employed in place of barium titanate and that the peak temperature is 2400" F., shows a resistivity below 800 megohm-centimeters, a dielectric constant of 69.5 and a power factor of 0.61%. Similar bodies containing magnesium titanate plus heavy grade titanium dioxide, or either beryllium titanate, aluminum titanatc or cerium titanate (either CeTIOI, or CeTizOc), plus heavy grade titanium dioxide or rutile, as in Examples 1, 3 or 4 below, show results which are in every case inferior to bodies containing no titanates. Bodies contain-' ing copper titanate are even worse.

Although 11; is possible to fCIIIl titanates at firing temperatures by adding compounds other than the titanates, such as the oxides, to titaniurn dioxide, it is not desired to do so for the reason that the reaction taking place usually involves the evolution of gas, For example, barhuu oxide exposed to the air will form barium carbonate, which at high temperatures will react to form barium titanate with the evolution or carbon dioxide. The evolution of gas causes a very undesirable bubbling or gas porosity in the ocramic, which cannot be entirely removed even upon prolonged firing. Such porosity renders the ceramic very undesirable for dielectric purposes. The effect of adding the titanates to titanium dioxide bodies in accordance with the present invention may be visualized more clearly by the tables which are appended to the subsequent examples. The titanium dioxide utilized in the various examples show the following analyses:

They are prepared as follows:

Heavy grade TiOz aevmsa tion of any monazite that may be present. The concentrate, consisting chiefly of a mixture or zircon and rutile grains, is then passed over a high power induction magnet, which separates about to oi the zircon from the rutile, leaving a pure zircon traction and a rutile fraction containing considerable zircon. The rutile fraction is then passed over an electrostatic separator, activated by a modified Wimshurst generator and controlled by gas discharge tubes. By means of successive passages over the electrostatic separator a rutile of the required degree of purity is easily obtained. This pure concentraue is then suitably comminuted by grinding in a porcelain lined ball mill (or in iron equipment iollowed by acid leach to remove iron introduced in milling), to particle sizes varying from 0.5 to microns.

Rattle B This material is prepared in the same general fashion as rutile A except that the grinding is carried to particle sizes varying from to 8 microns.

For the purposes of comparison, a titanium dloxide body and a rutlle body containing no titanates were prepared as follows: 1 kilogram of heavy grade titanium dioxide and l kilogram of rutile B, respectively, are separately thoroughly mixed with 10% by weight of 5% gelatin solution and passed through a 20 mesh screen. 125 grams or each batch is placed in the cavity of a steel mold. of l inches in diameter and the specimens formed under pressure oi 1200 pounds per square inch. The bodies are then fired according to the following schedule: the heavy grade titanium dioxide body is brought to a tem perature of 2300 F. and the rutilc body to a temperature of 2400 F., each at the rate of 50 F. per hour. They are held six hours at the peak Pigment grade TiOz of suitable purity .is heated, without other preparation, to a temperature 01' 1350 C., and maintained there for several hours. The resulting material shows well-deflned crystals of an average particle size or about 2 microns.

Rutzle A Australian sand deposits containing a suitable quantity of high grade rutile are first freed from quartz, sea shells, calcite, organic dirt, etc. by zravity separation over a wet Wilfley table. The use or fresh water serves to eliminate soluble impurities, such as salt. The concentrate is then dried and passed over a low power magnet which removes magnetic minerals, such as chromite, il

manite, magnetite and to a certain extent a portemperature, the temperature then descreased at the rate of 50 per hour to 1200 F., then at the rate of F. per hour from 1200 F. to 800 F., and the furnace then shut down. Close textured bodies about 0.5 ems. thick and 8.76 cms. in diameter are produced.

Having described the invention the following examples are now given:

EXAMPLE 1 900 grams of heavy grade titanium dioxide and 100 grams of barium titanate (BaTioa) are thoroughly mixed by ball milling with water, dried and disintegrated. To this mixture 10% by weight of 5% gelatin solution is added and thoroughly incorporated and the batch passed through a 20 mesh screen. grams of the batch is placed in the cavity of a steel mold 4 inches in diameter and the specimen formed under a pressure of 1200 pounds Per square inch. The body is then fired according to the following schedule: it is brought to a temperature of 1800 F. at the rate of 50 F. per hour and then at the rate of 100 F. per hour from 1800 F. to the peak temperature (2300 F.). The body is held at the peak temperature for six hours. The temperature is then decreased at the rate of 100 F. pe hour to 1800 F. and the furnace then shut down. A close textured body about 0.5 cm. thick and 8.68 cms. in diameter is produced.

EXAMPLE 2 The same procedure is followed as in Example 1 except that rutile A is used in place of heavy grade titanium dioxide, and that the peak temperature employed is 2350 F.

H. G. T10, llutlla 'I'xau VI Resist. mln

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5 fills the necessary qualifications.

As many variations are possible within the scope of this invention, it is not intended to be limited except as defined by the appended claims. The term alkaline earth as used in the present the elements calcium, barium and strontium only.

We claim:

21.. The method of forming a ceramic dielectric perature a composition containing 80 to 07% of titanium dioxide and 3 to 20% of a. preformed material taken from the class consisting oi calcium titanate, strontium titanate, barium titanlead titanate.

2. The method of forming a ceramic dielectric material comprising firing, at an elevated temperature such as to obtain maximum vitreous substantially no crystalline growth, a composition containing 80 to 97% of titanium dioxide and 3 to 20% bf a preformed material taken from the class consisting of calcium titanate, strontium titanate, barium titanate, cadmium titanate, zinc titanate, and divalent lead titanate. v

3. The method of forming a ceramic dielectric material comprising firing at an elevated temperature a composition containing 80 to 97% of tanate.

With

In the The value In the case Example number at m l m P mm m rum m F 000000000 oon-11m m I D P a ammo a as H P t n w e m 0 n e S m 0 V R. 0943072 ru 7 hm m ammu 2mm010543 n a O h h 2 0 838880 b a a v. f. l n m 0 e mmmmmmmwww mm m emw m m m W cuuuunruodo m i h m m r t i a m mm a a m a emnm o oe nu m H M w cl n m C r. E IN S S n e w m mm m mw am mmmd hm T n 0 e 8 S D. b V V S h t a I U emummmc a d em mthm m m w m f. .Et 8 B O r C r u m M M P .t. m t .B W H X e S n a H m m wmim e n t O .l T h n S t 0 m 8 m t a .1 a n H m Ym W i .w e U 1 S mm 8 Mm m W a m B m tm It 0 2 3 4 "23 .14 .11 4 m "mmmnmmwe M w m mamnmamm 446423355 m m mcstt wad Wmwmaamwaa a a m m omemade t sso m m m 5 1 .3? MMMMMWWWW m u H rflfifimwmmmu 111111 TA u w m m m astt r3232; m n a aannnmms flalh waazam .388 8388 X l E 4297 cm3 I terstat aaamwmnm nnwmmmmmww U nlllwkllll m814537490 maamaamaaa m rst as m mwmmmmmumm m m t u u M m u m m m m m m w w m n n T u w d c c T W m l 1 It will be seen from the above tatiies that the dielectric characteristics of the ceramic materials in accordance with this invention are excellent. In most cases, in addition, these ex" to specification and claims is understood to include tremely satisfactory dielectric characteristics are some the change over a wide range is nil (i. e. the curve is flat) which is a very desirable quality in radio and television work. It will be noted that 45 material comprisin fl s at an elevated temthe ratio of the one minute resistivitics or the titanium dioxide body containing no titanate to the one minute resistivity of the rutilc body con- 01 most of the titanates added in accordance with to ate, cadmium titanate, zinc titanate, and divalent the present invention, this ratio is very much reduced. In the case of lead (Examples 9 and 10), the ratio is practically 1-'--1. In the case oi cadmium (Examples '7 and 8), the ratio is less than 2-1. In the case of barium (Examples 1 5 structure with case of strontium (Examples 3 and 4), the ratio is less than 3--1. In the case of calcium (Examof lead titanate in eliminating the effect of vanadium as an impurity is particularly noticeable. The titanates of the present invention may be used either singly or in combination. For example, by employing a mixture of lead titanate and strontium titanate, or lead titanate and 65 titanium dioxide and 3 to of strontium tibarium tltanate, or lead titanate and cadmium the characteristic of lead titanate in eliminating the eflect of impurities may be comchanged very slightly with temperature.

taining no titanate is about l.

and 2), the ratio is approximately 1 -1.

ples 5 and 6), the ratio is about 8--1.

titanate 4. The method of forming a ceramic dielectric material comprising firing, at an elevated temperature such as to obtain maximum vitreous structure with substantially no crystalline growth, a' composition containing 80 to 97% oi titanium dioxide and 3 to 20% of strontium titanate.

bined with the desirable electrical characteristics imparted by the other three titanates.

For purposes or comparison, the characteristics of the heavy grade titanium dioxide body and the rutile body containing no titanates, prepared 5. The method of forming a ceramic dielectric material comprising firing at an elevated temas described above, are given in Tables VI and VII following perature a composition containing 80 to 97% of titanium dioxide and 3 to 20% of divalent lead titanate.

8. The method of forming a ceramic dielectric maerial comprising firing, at an elevated temperature such as to obtain maximum vitreous structure with substantially no crystalline growth, a composition containing 80 to 97% of titanium dioxide and 3 to 20% of divalent lead 10 tifanate.

EUGENE WAINER. NORMAN R. THIELKE. 

